For weeks, smoky, unhealthy air from large wildfires has plagued much of the West Coast and beyond. What's the public health impact of an increase of urban wildfires, in which homes and other structures burn? Special correspondent Cat Wise meets some of the researchers studying the risks for people from smoke and ash.

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William Brangham:

Now to another story about extreme weather and its impact.

Wildfires have plagued Northern California and the Pacific Northwest this year. In California alone, some 6,400 fires burned nearly one-and-a-half million acres.

Most destroy wildlands, but, as special correspondent Cat Wise reports, some urban areas are increasingly under threat. And it's not just a danger from fire. Researchers are trying to understand the risks from all that smoke and ash.

Cat Wise:

Last October, this was Santa Rosa, California's Coffey Park neighborhood. Today, nearly a year later, it looks like this. Crews of busy construction workers are rebuilding hundreds of homes. Nail by nail, communities around the region are rising from the ash.

But there are questions about what was in that ash and in the air above that could impact residents long after the rebuilding is done.

On a recent morning, air pollution scientist Keith Bein drove through the streets of Coffey Park hauling two small electric vehicles and some equipment he hopes will help him eventually answer some of those questions.

These Mercedes smart E.V.s are a key part of the prototype system Bein has designed to get better air quality information to the public in the aftermath of a wildfire. Think storm chaser, but instead of looking for tornadoes, he's chasing wildfire smoke.

Keith Bein:

Well, I call this the rapid-response mobile research unit. We can deploy this thing at the drop of a hat, and we can go anywhere we want to. There doesn't have to be power.

Cat Wise:

Each vehicle can run his sophisticated air sampling equipment for 18 hours.

Keith Bein:

I'm going to flip a switch to turn it on. There it goes.

Cat Wise:

Bein is part of a University of California at Davis collaborative research project looking at the short-term and possible long-term health impacts from the North Bay wildfires.

The study is funded by the National Institutes of Health, which is also a "NewsHour" funder.

After spending several days sampling Redding in the Carr Fire, he brought his mobile lab to Santa Rosa to see what might still be lingering in the air.

Keith Bein:

The wildfires that I sampled from Napa and Sonoma were this off-white, tannish color that I had never, ever seen before. When you have new situations like this, these urban wildfires, now you're just — any consumer product, cars, paint, cleaners, construction materials, you name it, it's all going up in flames.

Then all of those emissions are going to be very different both chemically and most likely toxicologically, compared to what we normally study as very isolated wildfires.

Cat Wise:

His samples will be tested back in a lab for toxins like meddles and organic compounds from products like pesticides, but eventually he wants to provide that kind of information in real time to residents.

Wildfire smoke is known to cause a host of health issues. And a growing body of research suggests it may contribute to thousands of premature deaths annually. But scientists fear those health impacts may be compounded if the smoke is more toxic.

Keith Bein:

OK, so this is going to be the great room on this side, kitchen right here,

Jeff Okrepkie lost the Coffey Park home he and his family had been renting for five years before the fires. He's eager to return and move on. But he's still thinking about those immediate days after the fires.

Jeff Okrepkie:

The first time we came back, stuff was still smoldering. Stuff was still warm. Then it starts to kind of sink in. I spent like eight hours on that property just kicking up ash. What's that going to do to me, you know?

Cat Wise:

He's also concerned about his young family's health. Just three days after the fires, he and his wife, Stephanie, learned she was pregnant.

Stephanie Okrepkie:

At first, I didn't bother putting the mask on, because I didn't know I was pregnant. But, then after the fact, I was like, OK, every time I stepped out, I had to put a mask on.

I don't think it filters 100 percent of all the particles that are out in the air.

Cat Wise:

Baby Quinn is now several months old. She's thriving, but her parents are wondering if her exposure in utero to wildfire contaminants may have an impact down the road.

That's a question also on the minds of two U.C. Davis public health researchers. Rebecca Schmidt and Mackenzie Oliver are enrolling women like Stephanie who were pregnant during or after the fires in a study. They're collecting bio-specimens, including cheek swabs, blood, breast milk, placentas, and hair, to assess toxins the women and their babies may have been exposed to.

Rebecca Schmidt:

What we have seen is that people are still having symptoms from this fire almost a year later.

Cat Wise:

Schmidt is the study's principal investigator. And she's also involved in a larger general health survey with about 2,000 participants.

Rebecca Schmidt:

As these fires become more common, and they're more likely to hit urban areas, we just need to know, what are the best actions to take to reduce the risk for some of these longer-term and short-term health impacts, so things like, when do we need to evacuate them?

Cat Wise:

Smoke, of course, is one byproduct of wildfires. Another is ash. Nearly two million tons of debris from four counties was cleared by contractors for the Army Corps of Engineers, but many areas remain untouched.

Karen Holbrook:

We had a sense of potential hazards that could be in the fire debris, and we're very cognizant of that. And that informed many of our actions.

Cat Wise:

Dr. Karen Holbrook works for the Sonoma County Department of Health. Despite the enormity of the disaster, she says the department acted quickly to protect the public. She believes there should be ongoing studies of health impacts, but she's not worried.

Karen Holbrook:

My sense is that, over the long term, this level of concern for a broad toxicity is overstated. I live here. I'm feeling comfortable about it. I do — there is — there was some that went up into the air and settled down. And it is going to work its way in.

But I don't believe — truly, I don't believe that it's at a level where it's going to cause harm over the long term.

Cat Wise:

The county health department didn't collect ash samples. But another team of Davis Scientists did.

The instrument measures the masses of ions that are coming through.

Professor Tom Young and grad student Gabby Black are currently testing samples from both wildland areas and former homes that Black collected last fall in her native Sonoma. The results so far show a big difference between the two.

Tom Young:

We see thousands of compounds in the household samples that we don't see in the wildland samples. The vast majority of those, we cannot yet say what they are, and we can't say what their toxicity is.

Many of them are not necessarily a cause for concern. The diversity of organic chemicals, our body is designed to deal with a lot of that. The problem is, it doesn't deal with all of it.

Cat Wise:

Of all the threats to public health now being studied, one became immediately clear after the fires, contaminated water.

In Santa Rosa's Fountaingrove neighborhood, benzene and other chemicals from melted plastic pipes leached into the water supply.

Bennett Horenstein:

It really wasn't something that had ever been considered or found to be an issue following a fire like this.

Cat Wise:

Bennett Horenstein is the director of Santa Rosa Water.

Bennett Horenstein:

And as these homes unfortunately burned, the plastic burned and gave off chemicals. And that happened, also, coincidentally, with losing water pressure. And that allowed this contaminated water in the homes to come deep into our water distribution system.

Cat Wise:

The water district has been replacing damaged service lines at about 400 sites with safer, but more expensive copper piping; 250,000 gallons of water a week are now being flushed through the system to clear the chemical. And water testing is happening regularly.

Back in Coffey Park, Jeff Okrepkie says the recovery of his community will continue long after the last house is rebuilt.

Jeff Okrepkie:

We are going to be, unfortunately, the poster child for fire recovery in a large scale for the next who knows how many years. We're already seeing it with what happened in Redding. People are coming to us and like, where are you guys a year out?

And I think we need to be the ones that are at the forefront of attacking these public health concerns and making sure we have answers.

Cat Wise:

Okrepkie hopes to be in his new home by next spring. U.C. Davis researchers hope to start releasing some of their results later this year.